Which expression defines the arithmetic series 1 + 5 + 9 + . . for seven terms?

Step-by-step explanation:

Given :  arithmetic series 1 + 5 + 9 + . . .

To Find: Which expression defines the arithmetic series 1 + 5 + 9 + . . . for seven terms?

Solution :

1 + 5 + 9 + . . .

a = first term = 1

d = common difference = 5-1=9-5=4

Formula of nth term =

So, formula for nth term for given sequence  

So,    defines the arithmetic series 1 + 5 + 9 + . . . for seven terms

Now, formula of sum of n terms in A.P. =

So, the sum of seven terms in given series =  

                                                                      =  

                                                                      =  

                                                                      =  

Thus the expression for the sum of seven terms =

b.) 160 miles on a 5 gallons car

step-by-step explanation:

240/10=24 miles/gallon

160/5=32 miles/gallon

30/1=30 miles/gallon

168/6= 28 miles/gallon

32 miles/gallon is the most amount, so this is the best.